1. Field of the Invention
The subject matter of this invention relates to those devices which perform mensuration and particularly those which are adapted to determine microscopic lengths. It is most closely related to those devices which employ a television image of the device as an aid to the operator in performing the measurement.
2. Description of the Prior Art
In the most widely known device employing electronic means such as a closed circuit television apparatus to display a magnified image of the object to be measured, the viewing screen of the television apparatus has superimposed on it in some fashion a grid pattern whose individual increments correspond to known dimensions in the field of view in which the object is located. By careful interpolation between the lines forming the grid pattern, the actual dimension of the object can be determined with reasonable accuracy. A modification on this scheme allows manual control of the position of a pair of markers in the displayed field of view on the television monitor screen. The distance between the markers is electronically correlated to the actual corresponding distance in the field of view and the numerical distance between the markers can be automatically displayed. By properly manipulating the position of the markers, the actual horizontal distance between any two features on an object in the field in view can be determined. Unfortunately, both of these devices suffer from two failings. On the one hand, judgment of the operator is required in interpolating between the grid markings and in positioning the markers. Since this requires subjective operator judgment, measurements are not always as precise as is desired. Secondly, inherent instability in the electronic apparatus associated with both these devices introduce additional errors. For these reasons, accuracy not as great as desirable for certain applications. This apparatus solves to a great extent, many of these problems.
The most closely related U.S. Pat. Nos. of which the inventor is aware are 3,737,856 (Lehrer, et al.); 3,645,377 (Troll); and 3,740,467 (Kubo, et al.).